1. Field of the Invention
The present invention relates to a hydraulic circuit for preventing a sudden movement of an actuator due to a rapid change in pilot pressure at the time of a rapid operation in a construction machine operating a control valve by the pilot pressure from a remote control valve and actuating a hydraulic actuator.
2. Description of Related Art
This type of a hydraulic circuit of a construction machine will be shown in FIG. 6.
In the figure, the reference numeral 1 denotes a hydraulic actuator (a hydraulic motor is shown as an example). The reference numeral 2 denotes a main pump serving as a hydraulic source. The reference numeral 3 denotes a control valve of a hydraulic pilot type for controlling an action of the hydraulic actuator 1. The reference numerals 4 and 5 denote pilot ports on the both sides of this control valve 3.
The reference numeral 6 denotes a remote control valve for operating the control valve 3. The remote control valve is formed by a pair of pressure reducing valves 7 and 8 and a lever 9 for operating the pressure reducing valves. Secondary sides of both the pressure reducing valves 7 and 8 are connected to the pilot ports 4 and 5 on the both sides of the control valve 3 through pilot tubes 10 and 11 respectively.
Pilot lines 12 and 13 for transmitting pilot pressure generated in the pressure reducing valves 7 and 8 to the control valve 3 via the pilot tubes 10 and 11 (pilot lines 12 and 13 indicating the whole pilot pressure supplying system including the pressure reducing valves 7 and 8, the pilot tubes 10 and 11, and the control valve 3) are formed. By these pilot lines 12 and 13, the control valve 3 performs a stroke action in accordance with a lever operation amount of the remote control valve 6 so that an action of the hydraulic actuator 1 is controlled.
In the figure, the reference numeral 14 denotes a pilot pump serving as the pilot hydraulic source, and T denotes a tank.
When the remote control valve 6 is rapidly operated in this hydraulic circuit, the pilot pressure transmitted to the control valve 3 by the pilot lines 12 and 13 is rapidly changed and the control valve 3 is rapidly actuated. Therefore, the hydraulic actuator 1 moves suddenly so that there is a problem of shock occurrence.
As techniques corresponding to this problem, Japanese Patent Laid-Open Nos. 2006-125627 and 2001-208005 are already known.
In the above techniques, throttle paths (a bleed-off path having a throttle, FIG. 6 shows an example of a throttle path diverged from the pilot tubes 10 and 11) 15 communicating with tanks T are provided in the pilot lines 12 and 13 (the pilot tubes 10 and 11 or a spool of the control valve 3, or the pressure reducing valves 7 and 8). By these throttle paths 15, a part of pilot oil is returned to the tanks while being throttled so as to exercise a buffering function of easing a change in the pilot pressure and preventing a sudden movement of the hydraulic actuator 1.
However, in both the techniques, since the throttle paths 15 are constantly opened over the entire spool stroke of the control valve 3, a leakage amount (a bleed-off amount) of the pilot oil is increased. Therefore, an opening area of the throttle path 15 is limited to be small so as to decrease this leakage amount as much as possible. Consequently, there is a disadvantage that a sufficient buffering effect is not easily obtained relative to an actuator action at the time of a rapid operation.
In consideration of not only a pressure decrease in the pilot lines 12 and 13 but also the leakage amount from the throttle path, the pilot pressure should be set to be high so that the spool of the control valve 3 surely reaches a stroke end at the time of a full operation. As a result, the spool reaches the stroke end before the lever 9 of the remote control valve reaches the maximum operation amount. Therefore, the lever operation amount is in excess so that there is a disadvantage of deteriorating operability.